1. Field of the Invention
The present invention relates to a system for detecting abnormalities in an image forming apparatus, and more particularly, to a system for detecting abnormalities which are liable to occur in an image forming apparatus and for judging the kind of abnormalities which have occurred.
2. Description of the Related Arts
According to an electrophotographic method, an electrostatic latent image formed on the surface of a photosensitive member is developed using toner contained in a two-component developer consisting of toner and carrier. A toner image is then transferred onto a paper sheet and fixed on the paper sheet.
A copying machine, a page printer and the like are provided as an image forming apparatus utilizing the electrophotographic method.
In order to optimize the quality of a reproduced image by controlling a developing process in the image forming apparatus, it is necessary to maintain the toner density, namely, the ratio between toner and carrier in the vicinity of a predetermined value.
To this end, a feedback control is performed by providing a toner density sensor in the vicinity of a developing unit so that the toner density sensor detects the density of toner accommodated in the developing unit.
A sensor for detecting the permeability of a two-component developer accommodated in the developing unit is widely used.
In an image forming operation, the two-component developer is regularly agitated and transported by a screw roller or rollers mounted in the developing unit so that the density of the two-component developer may be uniform. Therefore, a value detected by the toner density sensor corresponds to the value of the density of entire two-component developer accommodated in the developing unit.
The developing unit is often removed from the image forming apparatus for its maintenance and inspection, or for replacement of developer in the same color or in a different color.
When the developing unit is replaced with a new one, the toner density sensor is replaced as well because the toner density sensor is fixed to the developing unit. Therefore, it is necessary to check whether or not the toner density sensor is normal whenever the toner density sensor is replaced. This is because, as described above, the toner density sensor plays an important part in performing an image forming operation.
There is an increased demand for the development of a system capable of easily checking the abnormality of the toner density sensor.
Furthermore, when the developing unit is removed from the image forming apparatus, it is likely that a mechanism for transmitting the driving force to the screw rollers is damaged.
There is also an increased demand for the development of a system capable of promptly detecting a portion of the mechanism in which an abnormality has occurred.
Only the installation of a sensor or sensors for detecting the drive condition of the driving force transmission mechanism is not enough to accurately judge whether the abnormality has occurred in the driving force transmission mechanism or in the sensors.
The sensors occasionally become abnormal when the sensors are soiled by magnetic toner contained in the image forming apparatus.